C1q/Tumor Necrosis Factor–Related Protein‐9 Is a Novel Vasculoprotective Cytokine That Restores High Glucose‐Suppressed Endothelial Progenitor Cell Functions by Activating the Endothelial Nitric Oxide Synthase

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Abstract
Background: This study investigated whether gCTRP9 (globular C1q/tumor necrosis factor–related protein‐9) could restore high‐glucose (HG)‐suppressed endothelial progenitor cell (EPC) functions by activating the endothelial nitric oxide synthase (eNOS). Methods and Results: EPCs were treated with HG (25 mmol/L) and gCTRP9. Migration, adhesion, and tube formation assays were performed. Adiponectin receptor 1, adiponectin receptor 2, and N‐cadherin expression and AMP‐activated protein kinase, protein kinase B, and eNOS phosphorylation were measured by Western blotting. eNOS activity was determined using nitrite production measurement. In vivo reendothelialization and EPC homing assays were performed using Evans blue and immunofluorescence in mice. Treatment with gCTRP9 at physiological levels enhanced migration, adhesion, and tube formation of EPCs. gCTRP9 upregulated the phosphorylation of AMP‐activated protein kinase, protein kinase B, and eNOS and increased nitrite production in a concentration‐dependent manner. Exposure of EPCs to HG‐attenuated EPC functions induced cellular senescence and decreased eNOS activity and nitric oxide synthesis; the effects of HG were reversed by gCTRP9. Protein kinase B knockdown inhibited eNOS phosphorylation but did not affect gCTRP9‐induced AMP‐activated protein kinase phosphorylation. HG impaired N‐cadherin expression, but treatment with gCTRP9 restored N‐cadherin expression after HG stimulation. gCTRP9 restored HG‐impaired EPC functions through both adiponectin receptor 1 and N‐cadherin‐mediated AMP‐activated protein kinase /protein kinase B/eNOS signaling. Nude mice that received EPCs treated with gCTRP9 under HG medium showed a significant enhancement of the reendothelialization capacity compared with those with EPCs incubated under HG conditions. Conclusions: CTRP9 promotes EPC migration, adhesion, and tube formation and restores these functions under HG conditions through eNOS‐mediated signaling mechanisms. Therefore, CTRP9 modulation could eventually be used for vascular healing after injury.

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